Whoever says a carpet is "clean" after pre-spraying maybe needs to go on a refresher course
It ain't clean till the muck's been taken out!!
Yes, you're right. A bit of sloppy language use there.
What I meant to say was that the pre-spray, agitation and dwell time had moistened the fibres and soil and loosened the soil from the fibres and emulsified it so that the job of the HWE/LM is mainly to remove the soil-bearing emulsion. (So the fibers are clean (= free of attached soil), but coated in a soil-laden emulsion.) The carpet is, as you say, not clean until all the soil is removed.
If I understand (which I probably don't very well!!!) HWE removes the soil-bearing emulsion by high-pressure irrigation and vacuuming the liquid away. LM methods remove the emulsion by wicking it into an absorbent pad.
Although I understand that the friction of the water (in the case of HWE) and the pad (in the case of LM) on the fibres has an additional cleaning effect.